Heat treated agricultural implement disks having non-directional fracture characteristics



H. D. HOOVER 2,814,580 HEAT TREATED AGRICULTURAL IMPLEMENT DISKS HAVING Nov. 26, 1957 NON-DIRECTIONAL FRACTURE CHARACTERISTICS Filed Sept. 2, 1955 2 Sheets-Sheet 1 IiM/fi M07 56/02 I 17 0177/67 H. D. HOOVER 2,814,580 HEAT TREATED AGRICULTURAL IMPLEMENT DISKS HAVING Nov. 26, 1957 NON-DIRECTIONAL FRACTURE CHARACTERISTICS Filed Sept. 2, 1955 2 SheetsSheet 2 HEAT TREATED AGRICULTURAL IMPLEMENT DifiKS HAVING NON-DIRECTIONAL FRACTURE QHARACTERISTICS Helen 11). Hoover, Grand Marais, Minn., assignor to International Harvester Company, a corporation of New This invention relates to an improved article of manufacture. More particularly it relates to an improvement in agricultural disks having desirable structural properties.

In the tillage and cultivation of land, the implement disk plays an important part, whether it is used for plowing or cultivation. Because of difficult soil conditions, maintenance and Wear of the disks has presented a serious problem to the farmer and to the manufacturer. Disks during use may be subjected to extreme stresses due to severe impact conditions occurring when the disks strike boulders, rocks and other elements likely to be found in some soils. In order to overcome the severe fracturing of the disks, extensive research has been conducted and certain facts have become apparent.

Disks for agricultural uses may be stamped out of sheet steel which has been straight rolled, therefore imparting to the product a somewhat linear fibre or grain flow with the flow lines substantially parallel across the disk. The material generally used is a high carbon steel, and upon current conventional heat treatment the disk assumes a microstructure which is predominantly of tempered martensite. It has been found in the use of disks of this type that directional cracks will occur in the disk when subjected to severe conditions. Such cracks are directional in that they tear linearly along the fibre flow in the direction of their rolling pattern. Directional tearing of the disks in this manner generally results in large chunks of metal breaking from the disks so that they are completely inadequate for further use. Thus when a disk is damaged in this manner the operator must immediately replace the same.

To alleviate this condition a prior art process includes the rolling of the metal in criss-cross or cross rolling relation. Hardened disks which have been manufactured by the cross rolling method have indicated a lower propensity toward directional failure once a crack starts at the edge of the disk. Thus in certain cases of fracture, only small portions would tear from the edges of the disks and though the disks would be defective they could still be used for a period of time. Thus the only improvement in the art with relation to agricultural disks has been the development of a rolling process which results in a fibre flow design having improved properties preventing to some extent the directional tearing of the metal disks when it strikes an obstruction.

Cross rolling of disks, of course, requires additional machine and operator time which considerably adds to the expense of manufacture. In addition the complete absence of directional fractures is not found to be answered by this process.

It is a prime object of this invention, therefore, to provide an improved agricultural implement disk.

It is another prime object to provide an improved implement disk having increased wear life resulting from increased strength and a decided absence of directionality of fracture upon the disk being damaged.

A still further object is to provide a heat treated im- States Patent 2 plement disk having a microstructure consisting primarily of upper bainite, and without martensite.

Still another object is to provide an improved implement disk having the characteristic of non-directionality of fracture upon the disk being subjected to stresses beyond its normal capabilities.

Another object is to provide an improved implement disk that has been manufactured from a straight rolled or cross rolled steel, the disk having been austempered,

and having inclusions in its micro-structure which are relatively flattened, the disk having a highly desirable characteristic of fracturing in a random manner as distinguished from fracturing directionally or linearly along the fibre flow lines determined by the inclusions in the disk.

These and further objects will become more apparent from a reading of the specification when examined in connection with the accompanying sheets of drawings.

In the drawings:

Figure 1 is a side elevational View of an implement disk;

Figure 2 is a sectional view taken along the line 2-2 of Figure 1;

Figure 3 is an enlarged photograph of the microstructure of an austempered disk;

Figure 4 is a magnification photograph showing inclusions in the straight rolled disk of Figures 1 and 2;

Figure 5 is a photographic view showing the results of a ball fracture test on a conventional straight rolled disk;

Figure 6 is a photographic view of an improved austempered straight rolled disk showing the results of a ball fracture test.

Figures 1 and 2 show a conventional agricultural implement disk 10, of dish shape, having a cutting edge 11 and a hub portion 12. The cutting edge of disks of this type may include a number of arcuate shearing edges (not shown) and disks of this type are also in some instances of flat rather than dish shaped construction, the invention herein disclosed being applicable to all agricultural disks regardless of shape.

In manufacture the disks may be formed from a suitable billet which is flattened by rolling, or more likely the disks may be cut from sheet steel which has been rolled in a single direction, the terminology for such a process being straight rolled. Or the disks may be subjected to rolling mill techniques whereby the rolls pass in a plurality of directions over the metal, the terminology of such process being cross rolling. It is not deemed necessary to elaborate upon the manner in which the rolling is accomplished since such rolling is conventional and usually takes place between rolls under pressure through which the steel sheet or billet is fed.

In the straight rolling of disk steel the rollers pass over the steel sheet in one direction. The disk blanks are then cut from the sheets and subsequently formed into disks. By this process, as shown in Figure 4, the inclusions are substantially all linearly directed across the disk in substantially parallel fashion. The inclusions essentially comprise such elements as silicates, oxides, sulphides, and other non-metallic substances and in shape are generally long, and ribbon-like and are malleable at the rolling temperature. The inclusions are also said to determine or influence the fibre flow lines whereby in directional fracture or failure the metal tears linearly along the fibre flow lines.

By cross rolling the sheet steel the inclusions are flattened or widened, thelength however remaining substantially the same. This change in the shape of the inclusions is believed to be an important cause of the desirable results which have been obtained with cross rolled disks.

3 The chemical composition of a steel which has been pieces from breaking out of any disk. Small sections particularly satisfactory for implement disks and which is which break out on a non-directional disk will permit well adapted for the process hereinafter described may be the continued use of the disk for a period of time. as follows: Figures 5 and 6 show a conventional disk and an impercent proved austempered disk, both having been subjected to b 80 to 0 93 incl the approved ball test. In this test a hardened steel ball Car is forced through a drilled hole in the disk, the drilled Manganese to hole being of lesser diameter than the ball. Figure Phosphorous shows the directional breakage or fracture of a convenfii i i i' 10 tionally heat treated disk, and Figure 6 shows an im- QlllCOl'l (3.1.1 t0 v.30 lzlciproved austempered straight rolled disk indicating that Chromium Resluhai. b k 0 d f t f e n I ha t Nickel Residual. rea a e an rac ure is o a nonir c to a c Tic er. Mo] bdenum Residual. Repeated tests with the austempereddisks have s own y their superiority and freedom from directional .fracture. However, the process is also adapt t0 y Steel l Essentially then the present process contemplates the wmposiiion Which Will Produce satisfactory mechanical heat treatment of a high carbon steel disk which has been Properties when austempcrcd in a bath held at F, straight or cross rolled, the austenitizing of the disk and to 850 F. the subsequent isothermal quenching to produce a mi- While reference above has been mad t a Cr s rfllififi crostructure or crystal structure which is other than ausdisk, the improved P1139655 y be s practi ed W tenite or martensite, such as bainite with certain amounts 3 Straight Toiifid disk, thus eliminating a more Costly of pearlite, the heat treating process in conjunction with p h Y p g a disk Which has improved q the straight or cross rolling process, in combination, proties over any known disks. viding an improved structural change or result which is After the disk has been formed either from straight exemplified by random fracture of the disk as against rolled or cross rolled steel, the same is heated in a suitdirectional cracking or fracturing. able furnace or salt bath above the AC 3 (critical or Th i i apparent h an i d implement di k transformation) temperature into the austenitic state h b d ib d d one hi h h t d i h an (commonly referred to as austenitizing). The disks are austernpering process provides a completely new d 111611 qilinchfid in Bait bath held at a temperature of different desired result departing radically from known 650 F. to 850 F. until transformation has occurred processes of manufacturing disks. The objects of the infrom an austenitic to a primarily bninitic structure, withti h b f ll hi d d i must b d out martensite. This process of heat treating is also t d th t changes may b ad ith t de i f known as au rnp ring, wh h i fin in h mstallurgithe spirit of the invention disclosed or the scope thereof cal field as a hardening process based upon isothermal a defined in the appended claims. transformation of austenite to bainite. Austeinpering What is claimed is: takes place in this process wherein austenite is trans- 1, A h t t d t l implement di k h i iformed into bainite without intermediate production of marily bainitic microstructure, said disk having fibre flow martensite. lines extending linearly and substantially parallel The E. C. Bain Patent 1,924,099, August 29, 193 3, dethrough said disk, said disk having a fracture character- SCiilJeS the Process known as ailsiempermg which is p- 4.0 istic wherein during fracture the tearing of the disk is in plied to the present invention resulting in a new and a vari-directional manner relative to the fibre flow lines highly desirable implement disk. The patent concisely f the di k,

describes the process which consists primarily of ther- 2. A heat treated steel implement disk having a premally hardening a high carbon steel, quenching th dominantly bainitic microstructure, with inclusions theresteel from a temperature above the critical temperature in of a relatively fiat and elongated shape with a fibre bel w pp x m y 10000 but above h p grain flow extending linearly and substantially parallel ture of rapid martensite formation, and holding th Ste across the disk, said disk having fracture characteristics in such an intermediate temperature for a time inteival under severe stresses of cracking in a vari-directional sufficient to obtain substantial conversion of the austenite manner with respect t the fib grain fl f th di k,

to crystal structures other than martensite, namely bain- 3, A h t t d t l implement di k h i a ite. The process thus described is applied and included atively sharp peripheral ground engaging edge, said disk in the process of the present invention to provide the having a predominantly bainitic microstructure throughimproved result heretofore not contemplated. out a major portion thereof, and fracture character- Figure 3 shows typical microstructure of the steel in istics whereby during structural failure the disk cracks in a disk after the austempering process has been peravari-directional manner relative to the fibre flow strucformed. In addition this figure shows a certain amount ture of the disk.

of fine pearlite and transition products whichinay occur 4. A heat treated high carbon steel implement disk during the process but do not affect the desired characterhaving inclusions defining a generally linear and parallel istics of the austempered disk. Figure 4 Shows that th fibre flow structure and a predominantly bainitic micromaterial is straight rolled by the pattern of the inclusions structure, the said disk having fracture characteristics at which extend linearly across the disk in substantially ultimate stresses whereby the disk cracks in a vari-direcparallel relation. tional manner relative to the fibre flow structure of the The above process therefore results in a disk having a disk.

primarily bainitic microstructure. Actual field tests and ball tests definitely prove that a disk of this type after 55 References Cited in the file of this patent treating will have the desirable feature referred to in UNITED STATES PATENTS this application, non-directionality. This term means i i that when a fracture occurs in the disk, the fracture may 1924099 Bam at a] 1933 start parallel to the rolling direction or fibre flow lines, 2'395184 Hume et a1 1946 but progression of the fracture occurs in random or vari- OTHER REFERENCES directional direction with respect to the rolling direction or fibre flow. This result is particularly desirable in the field under severe service conditions since it prevents large Cold Working of Metals, A. S. M., 1949, pages 107 and 108. 

1. A HEAT TREATED STEEL IMPLEMENT DISK HAVING A PRIMARILY BAINITIC MICROSTRUCTURE, SAID DISK HAVING FIBRE FLOW LINES EXTENDING LINEARLY AND SUBSTANTIALLY PARALLEL THROUGH SAID DISK, SAID DISK HAVING A FRACTUR CHARACTERISTIC WHEREIN DURING FRACTURE THE TEARING OF THE DISK IS IN A VARI-DIRECTIONAL MANNER RELATIVE TO THE FIBRE FLOW LINES OF THE DISK. 